Telephone system



April 29, 1941. E. s. PETERSON TELEPHONE SYSTEM Originl Filed Oct. s, 1958 4 Sheets-Sheet 2 QQN QQFOMZZOD QUE/3 ohomzzou $95k Edward 5. Fel'ersmn; m-aa ma, M

ATTORNEYS.

April 29, 1941.

E. s. PETERSON TELEPHONE SYSTEM Original Filed Oct. 3, 1958 4 Sheets-Sheet 3 wvwh mwg mmmwm komu mum A $8 8% Qwww INVENTOR. Edward E. Fe'l'ersun mum NQQ $98k mm mm QR sow 3b mac NMU b QQQQ Eb OQN m bmzzob Patented pr. 29, E41

TELEPHONE SYSTEM Edward Sigford Peterson, Elmwocd Park, in, as-

signor to Associated Electric laboratories, Inc.,

Chicago, 111., a corporation of Delaware Original application October 3, 1938, Serial No.

233,021- Divided and this 1939, Serial N0. 282,106

19 Claims.

The present invention relates to automatic telephone systems and has ior one of its objects the provision of improved link circuit apparatus of the character generally used to establish connections between the lines oi a l automatic exchange forming e part of a. lerger telephone system. This application is a division of application Serial No. 233,021, filed October 3, 1938.

It is another object of the invention to provide in an automatic telephone system, a. switching link for setting up connections between the lines of the system and comprising a switch which is initially operative to select one of a number of characteristic sources of ringing current to be projected over a called line selected by the link and which is subsequently operative to time the interval during which an established connection between two lines of the system is set.

up by way of the link.

It is a further object oi the invention to provide, in an automatic telephone system oi the character described, a, switching for setting up connections between the lines oi the system and comprising a switch which is initially operative to select one of a number of characteristic sources of ringing current to be projected over 2. called lineselected by the link and which is subsequently operative alter a first time interval to transmit a warning signal over an established connection setup by the link between two of the lines of the system, thereby to indicate to the parties conversing over the connection that the connection has been held for a predetermined application June 30.

noting thereat and operative to set up connections between the lines, together with a distributcr tor assigning idle ones of the links to the use of calling ones or the lines in a. predetermined order. Each of the links comprises timing means including a. stepping switch. which is initially opthat the connection has been held for s' prede= time interval and is about to be released, and

which is finally operative after a second time interval to cause the link'to be released.

It is a still further object of the invention to provide. in an automatic telephone system, a switching link for setting up connections between the lines of the system which is so arranged that the above-described functions of selecting the character of the ringing current to be projected over a selected line, impressing a warning signs] upon an established connection routed by way of the link, and releasing the link a predetermined time interval after the connection routed by way termined time interval and will be forcibly res leased shortly thereafter. Finally, the arrangement is such that this switch is operative after a second time interval to cause the link to be re-' including. a switch for selectively connecting a selected source of ringing current to the called line, and means governed by the second control means mentioned above for controlling the switch.

Theexchange further comprises a. source of warnlng current and timing meansinciuding the abovementioned rinsing current selecting switch for connecting the source of warning current to a connection routed by way of the link and established between two of the subscriber lines a first predetermined time interval after the connection is set up. This timing means further functions automatically to release the link a second predetermined time interval aiter the connection routed byway of the link is established. In ac, cordance with a further -feature of the invention the link circuit isso arranged that the QbOVE-r mentioned switch, forming a part of the timing means, is also operative simultaneously to select the side 0! a called multiparty line over which ringing current is to be projected and the particular source of ringing current which is to be utilized in signaling the called substation associated with the selected line. 1

Further features of the invention pertain to the particular arrangement of the circuit 51 .switching links, including the illustrated finderments whereby the above-outlined and additional operating features are attained.

The novel features believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention. both as to its organization and method of operation, together with further objects and advanwhich may be interconnected with a distant central exchange, not shown, by means of a group oi two-way trunk lines including the trunk line The suboflice 50 includes a plurality of connector link 60, for setting up connections between the lines extending thereto. More particularly, the suboflice has an ultimate capacity of one hundred lines, including two groups of trunk lines of as many as ten lines each. Obviously, the number of trunk lines in each group is determined by the amount of, interoillce trafiic routed by way of the automatic switching apparatus provided in the subofilce 50, three trunk lines in each group being suilicient for reasonably good service. Each of the links provided in the suboince may be identical to the link I50, which comprises a finder portion llll and a connector portion 200, each having access to the lines terminating at the subofiice. Preferably, the links are arrangedin first and second groups, each group being provided with a. distributor individual thereto for assigning idle ones of the links in the group to the use of calling lines. The number ,of links included in each group is determined by the amount of traffic which the suboilice 60 is required to handle, and reasonably goodservice may be rendered when each ofthe two groups of links includes five links. The first group of links, including the link 60, is provided with a. link distributor 100. The lines terminating, at the subofiice 50 are also arranged in first and second groups, which groups are individually associated with corresponding ones of the distributors, whereby calling lines in the-first group of lines are normally assigned for use idle ones of the links in the first group of links, and calling lines in the second group of lines are normally assigned for use idle ones of the links in the second group of links, thereby rendering it possible simultaneously to extend two calls respectively initiated on two lines individually included in the two groups of lines. Further, the distributors are. so connected-and arranged that a call initiated on a line in theflrst group of lines is assigned for use an idle link in the second group of links in the event that all of the links in the first group of links are busy. Similarly, a call initiated on a line in the second group of lines each arranged to serve a number of subscriber substations respectively including the substations A, B and C, D. Each of the indicated substations is provided with a telephone instrument,

' a calling device of the dial operated type, and a prises a line relay Ri55, a cut-oil. relay RIBO and a slow-acting lockout relay RISII.

Preferably each of the links is connected and arranged in a manner similar to that of the link 60 which comprises the finder switch llll and the connector switch 200, each of these switches including a switching mechanism of the Strowger type. The Strowger mechanism included in the finder switch H, as best shown in Fig. 1, comprises a bank of fixed contacts I02 arranged in ten vertical levels, each level including ten radially disposed contact sets, each terminating a line extending thereto, a wiper set associated with the contact bank l02'and carried 'by a carriage movable in both vertical and rotary directions, a

row of fixed contacts [04 arranged in vertical alignment, each terminating acontrol conductor,

and a contact wiper associated with the row of contacts I04 and carried by the movable carriage. Also this Strowger mechanism includes a vertical magnet M105 for' moving the carriage in the vertical direction, a rotary magnet MI 05 for moving the carriage in the rotary direction, and a release magnet MI 01 for releasing the carriage and returning it to its normal position. Also associated with this Strowger mechanism are a set of switch springs I08, which are actuated by the movement of the carriage in a' vertical direction away from its normal position, and a' set of switch springs I09 which are actuated by the movement of the carriage into the eleventh radial position. Also a finder switch lfll comprises a switching relay RIM and a control relay RI.

The Strowger mechanism included in the connector switch 200, as best shown in Figs. 2 and 3.

comprises a bank of fixed contacts 300 arranged in ten vertical levels, each level including ten radially disposed contact sets, each terminating position. Also associated with this Strowger mechanism are two sets of switch springs 209 and 345 which are actuated by the movement of the carriage in the vertical direction away from the is assigned for use an idle link in the first group of links in the event all of the links in the secnormal position, two sets of switch springs 2H) and 338 which are actuated by the movement of the carriage in a vertical direction to the level of contacts in the'contact'bank 300 terminating the lines in the-second group of trunklines, and a set of switch springs 249 .which are actuated by the movement of the carriage in the vertical direction to the level of contacts in the contact Each of the lines extending to the subof trunk lines. It is noted that the first group of trunk lines terminate in the tenth level of contacts in the contact bank 300 of this Strowger mechanism; the second group, of trunk lines terminate in the ninth level of contacts in the contact bank 300 of this mechanism; and the subscriber lines terminate in the first to the eighth, inclusive, levels of contacts in the contact bank 300 of this mechanism Furthermore. it is noted that the Strowger mechanism included 2,239,902- bank 300 terminating the lines in the first group in the connector switch 200 is of the automatic trunk hunting type; via, an idle line in the first group 01" trunk lines is seized thereby when the single digit is dialed into the connector switch tial and the front contact associated with the armature RA305 oi the switching relay R395.

Furthermore, the connector switch 200 comprises a group of relays and their control and controlled circuits, this group of relays including aline relay R200, a hold relay. R255, a cutthrough. relay R200, a battery reversing relay R250, a ring cut-oil relay R350, a test relay R310, a ring control relay R300, a switching relay R395, and a number of control relays R2 l0, R220, R225, R350, R210, R200, R345, R350, R355, R380 and R 0 A first timing arrangement is incorporated in the connector switch 200 which causes the con- 200, and idle line in the second group of trunk lines is seized thereby 'when the first digit 9 followed by a predetermined second digit is dialed into the connector switch 200. Also a particular subscriber line is seized and rung by the connector switch 200 when the three digits corresponding to the directory number of the'particular subscriber line are successively dialed into the connector switch, regardless of whether the particular subscriber line is the calling subscriber line, which is seized on a reverting call, or an independent subscriber line. In calling a particular subscriber line, the first and second digits dialed into the connector switch 200 correspond to the position of the subscriber line in the contact bank 300 of the Strowger mechanism included therein, while the third digit dialed into the-connector switch determines the character of the ringing current to be projected over the seized line and the type of ringing circuit to be used, as is more fully explained subsequently.

The connector switch 200 also comprises a minor switch 325 which includes three rotary switches 325, 330 and 334, each including a con-' tact bank and an associated wiper, the contact banks of these switches being indicated, respectively, at 323, 333 and 331-, and the associated wipers thereof being indicated, respectively, at 321, 33l and 335. The minor switch 325 also includes a rotary magnet M305 for driving'the wipers of therotary switches and a release magnet M343 for releasing the minor switch so that the wipers of the rotary switches may be automaticaly returned to their normal positions. Also associated with the minor switch 325- is a set-0t switch springs 330 which are actuated by nector switch to be released and a calling line associated therewith to be locked out, in the event the connector switch is not completely operated to select a line terminating threat, after it has been seized by the calling line. A second timing arrangement is incorporated in the conhector switch .200 which is operative to warn the subscribers that an established connection in-' tional time interval.

ed therein fails to restore completely after it has the movement of the wipers oi the rotary switches thereof away from their normal position. The minor switch 325 is utilized to select the particular frequency or code 'of the ringing current, depending upon whether harmonic or code ringing is employed in the system, to be projected over a line seized by the connector switch 200 and to select the particular conductor over which. the r ng current is to be projected in the event a divided ringing circuit is employed in the system. Certain alternative wiring is provided including the wiringillustrat'ed at "X" and Y in Fig. 3, which is connected in a manner more fully described subsequently in order to accommodate ,ithe use of the connector switch 200 to different types of ringing employed in the system. More particularly, the "X wiring is utilized when code ringing is employed in the system and comprises a connection between the ring pick-up lead C322 and the front contact associated with the armature RA300 oi the switching relay R305. On the other hand, the Y wiring is utilized when harmonic ringing is employed in the system and been released.

Preferably, each of the distributors is connected and arranged in a manner similar to that of the distributor individually associated with the first group of links which comprises, as best shown in Fig. 7, a rotary'switch including four banks of fixed contacts and four wipers individually associated therewith, the correspondingcontacts in each bank terminating the control conductors extending to the respective links in the first group of links and the wipers terms nating the control conductorsextending to the distributor. Also the rotary switch 105 includes a rotary magnet M101 for driving the wipers associated with the contact banks. The distributor 100 also comprises a startrelay R120, a

switch-over relay R1I0, a test relay R, a

number of control relays R115, R135, R140, R150, R and R100, and the control and controlled circuits therefor.

Also associated with the distributor 100 are a signal lamp 122, which is illuminated in the event the finder switch of the link assigned by the distributor to the use of a calling line does not find the calling line'within a predetermined time interval, and a signal lamp 123 which is illuminated in the event that the carriage of the Strowger mechanism included in the finder switch of the link employed in an established number of calls which are extended by way ofthe links in the first group of links associated with this distributor.

The distributor 100 is so connected and arranged that a second idle link in the first group of links is assigned to the use of a calling line comprises a connection between ground poten- 75 in the first group of .lines, in the event that a first idle link in this group assigned thereto fails,

to find the calling line during the course of operation thereof. Alsoa testing arrangement comprising a switch 102 is provided in the distributor'100 in order to provide for automatic testing of the finder switch of each link in the first group of links.

The distributor 100 is of the preselective type in that an idle link in the first'group of links is selected tobe assigned to the use of a calling line in the first group of'l-ines prior to the initiation of a call on a line therein, and another idle transferred to the distributor associated with .the

second group of lines, whereby the second-mentioned distributor assigns idle ones of the links in the second group of links to the use of the calling lines in the first group of lines.

Ordinary substatidn to substation calls within the subojfice An ordinary call which is to be extended from one subscriber substation to anotherwlthin the -s'uboifice is initiated at the calling substation by removingthe receiver of the telephone instrument thereat from its hook. For example, in extending a call from the subscriber substation A to the subscriber substation C within the suboifice 50, the call is drstinitiated at the substation A by removing the receiver of the telephone instrument thereat from its hook, thereby to complete a bridge path at the telephone instrument at thesubstation A between the line conductors Cl I6 and CI I1 of the subscriber line .I II extending to the substation A. When this bridge path is completed between the line conductors of the subscriber line 5 a circuit is completed for energizing the line re1ay,RI55 in the line circuit I individually associated with the subscriber line H5, which extends from battery at the upper winding of Rl55 by way of the. upper winding of RISS, RAIGZ, CHO, the bridge path between CH6 and CH1, CII1, RAI63, and the lower winding of RI55 to ground. When energized over the above-traced circuit the line relay RI55 operates tocomplete, at RAISE, an obvious path for applying direct ground potential to the control conductor CI I0 of the subscriber line H extending from the connector switches of the links having access thereto, thereby to mark the subscriber line I I5 as busy to the connector switches. pletes, at RAI58, a'path for app y l 'plmd RAIN and the back contact associated therewith, C100, and the resistor I00 to the start conductor CI01. It is noted that the contact I04 is the first contact in the contact bank I04 oi the 'Strowger mechanism included in the finder switch Ill. Accordingly, the subscriber line I10 is terminated in the-first level in the contact banks oi the Strowger mechanisms included in the finder switches of the first group or links. Also, upon operating, the line relay R155 completes, at RAI 01, a path for applying battery potends! to the control conductor CI l0 oi. the sub- .is rib r line 5, thereby to mark the radial po- Es'ition ot the contactsets in the contact banks of the Strowger mechanism included in the finder switches of the links terminatingthe suband RAII'I. to Cl I8.

This application of ground potential to the start lead CH1 extending to the distributor 100 completes a circuit for energizing the start relay R120, which extends from the grounded start lead C101 by way of RA1 I 0 and the front contact assoelated therewith, and the winding of R120 to bat- ;tery. When energized over the above-traced circult the start relay Rm operates to initiate operatlon or the distributor 100, thereby to cause the idle one of the links in the first group, pre- .viously selected by the distributor 100, to be asthe signallamp 122, which .circuit is complated by apparatus, not shown, in the event the .start relay R120 remains operated for a predetermined time interval indicating that the callin subscriber line III has not been seized by the finder switch of a link in the first group or links Also the line relay RIBS compotential to the conductor Cl. thereby to mark with ground potential in the contact banks of the Strowger mechanisms included in; the finder switches of the first group of links, the level in T which the subscriber line H5 is terminated. and

path for marking thelevel in the contact bank I04 of the Strowger mechanism included in the from ground, at-RAI50, by way ofRAI" and the back contact associated therewith, one and CH5 to the contact I04 inthe contact bank I04, The path for applying ground potential to I the start lead Cl31, extending to the distributor finder switch "ll of the link illustrated extends within a predetermined time interval. Also the start relay R completes, at RA120, a circuit for energizing the rotary magnet M10I of'the rotary switch 101 in series with the relay R140,'this circuit extending from ground, at RA150, by way of HA1, RAIN, the winding of R140, RA1I I, the self-interrupting contact MA10I of the rotary magnet M101, and the winding of M10I to battery. When the above-traced series circuit is completed the rotary magnet M10l does not operate due to the high series resistance of the winding of the'relay R140. However, the relay R operates. Upon operating, the relay R140 prepares, at .RA141, a holding circuit, traced hereinafter, for energizing the winding thereof and completea'at RA140, a path for applying ground potential to the control conductor C140, thereby to initiate operation of the finder switch of the previously selected idle link in the first group.

Assuming that the illustrated link 60 in the first group 0! links is the idle link previously selected bj the distributor 100, this application of ground potential to the control conductor C140 completes circuit for energizing the relay R400 in the v der switch III of this link, this circuit extend- Y ing from the grounded control conductor C140 by way of the wiper 104 and the associated contact 100 in the rotary switch "10I, the conductor CH4, and the of R100, to battery. Also the relay R140 prepares, at RA142 and the front associated therewith, ,a circuit, traced hereinafter, for energizing the rotary magnet M10I oi therotary switch "I, and completes, at

7 .v extends from ground, at RAIN, by way. of 75 RAM], a holding circuit for energizing the relay R'II'II, the latter circuit extending from ground, atRA'HI, by way of C182 and the winding of .Rllfl .to battery. This holding circuit for the relay R'I'Iii retains this relay in its'oper'ated position during the operation of the distributor I I00, thereby to prevent.the relay R'Hll from recomplete, at RAISI, the holding circuit for energizing the relay R140, this circuit extending from ground, at RA'ISI, by way of RA'IH, the winding of mm, RAH I, the self-interrupting contacts MAID-Inf the rotary magnet M'liII and the winding of M 'IBI to battery. Also the relay R150 prepares, at RATSI, a holding circuit for energizing the lower winding of the test relay R730, and 325 (sets its own weighted armature RAISE into vibration, thereby to complete intermittently, at

RAISE, thecircuit for energizing the lower winding of the relay R155, this circuit extending,

to battery. ,The relay R756 is of the slow -tooperate type and does not operate at this time due to this characteristic and the fact that the circuit'for energizing the lower winding thereof ,35 is only intermittently completed, at BMW and When energized over the previously traced aircuit'the relay R 188 in the finder switch Et'ii oper ates to int-empt, at RAIN and the'oach contact associated therewith; the path for applying ground eotentielin'the finder switch M l to the all trunks husy conductor -Zit-thic'time multiple ground potential in the remaining idle links" in the first green or links is auhlied'to the A all trunks husy'conductor Citt, thereby to re tain the relay arts in its operated position suhsequent to the restoration of the relayfilfidto interrupt, at RAlgtlgthe holding circuit oi. the relay RIll. z-llso' the relay Rite completes, at (to RAW t and the front contact associated therewith, an obvious path'for applyin around no tential to the control conductor C1323 extending from the flnder-switch'tdt into'the associated connector switch 2%. This application of ground .55 potential to the control conductor CIZE also prepares a circuit,- traced; hereinafter, for energizing the lower winding of the relay RIM. Further the relay RIIQD interrupts, at RAItS and the back contact associated therewith, the connec- 580 tion between the control conductor CIE?! and the guard conductor CIIII, thereby to prevent the, operation of the rotary magnet M'ItI oi the retar-y switch MI inthe distributor wflprior to the operation of the finder switch it! to seize the calling subscriber line HE, this connection he'- tween the control conductor C523 and the guard conductor C'EtL-prior tointerruption, extending from the" control conductor CI23 byway of the switchsprings HE and Hit of the vertical oflnormal springs m8, RAiQt and the back contact associated therewith, and-CH3 to the guard conductor C3 33; Further the relay RIQEB prepares, at RAIQQ, and at RAIBS and the front contact associated therewith, a cir cuit,. traced herein- .75

after, for energizing the rotary magnet M10] 01' the rotary switch "I in the distributor I00 subsequent to the'operation of the finder switch Ifll to seize the calling subscriber line III, and prepares, at RAIM, a circuit,

traced hereinafter, forenergizing the rotary magnet MIIIG of the-Strowger mechanism included in the finder switch IM. Finally the relay RIW completes, at RAI9I, a circuit for energizing the vertical magnet MIII5 of the Strowger mechanism included in the finder switch iflfl, circuit extending from ground, at RA'IEE, by way of BAT, RAISI, RA'I3I and the back contact associated therewith, C142, the wiper W5 and associated contact I09 01' the rotary switch m, 0M5,

RAM E, and the winding oi Mlllli to battery. When energized over the above-traced circuit the vertical magnet Milli operates to more the carriage of the Strowger mechanism included in the finder switch IIII one step in the vertical direction, and to complete, at MAME, a circuit for energizing the relay R760, this circuit extending from ground, at MAIOB, by way of CNS, and the windingof am to battery. Also, at Males, the vertical magnet MI 05 prepares a circuit for short-' clrcuiting the upper winding of the test relay 1 R180, this circuit extending, when completed, .from ground, at MAME, by way of CH6, RA'ME, the upper winding'of R130, M133 and the back when completed, from ground, at RA'IEZ, by way of WA IEZ, BAT, and the lower winding of met contact associated therewith, C143, the wiper Hi2 and associated contact N5 of the rotary switch WI, CH0, and the control wiper to the associated grounded contact in the row of contacts 884 in the contact bani: oi the Strowger mechanism in cluded in the finder'switch IBI. When the carrlage of the Strowger mechanismincluded in the finder switch IN is moved one stepin the ver- .ticaldirection, the vertical ofi-normal springs +168 associated therewith are actuated, thereby to prepare, at the switch springs; M3 and tie thereof, a circuit traced hereinafter for energiztlie reiease magnet-HEWI- oi the Strowger mechanism-included in. the finder switch Hit, and to prepare, at the contact springs Ho and .E flu thereof, a circuit traced hereinafter for energizing the rotary magnet Mitt oi the rotary swii'ich MAME, the previously traced circuit for energizing the relay R and the previously traced preparfi path for short-circuiting the upper-winding of the relay 3139.; The relay-R189 then; restores to recomplete, at RAI6I,.-the previously traced circuit for energizing the vertical magnet MEGS of the Strowger mechanism included in the finder switch icL- Theyertical magnet MW! and the relay R756 continue to interact, as described above, until the carriage of the Strowger mechanism-included In the finder switch MI is moved in a-yertical direction to the level in which the eailiw subscriber line is terminated. Iii-the present instance thecalling subscriber line II 5 is terminated: in the first leveL- Accordingly, the vertical magnet MIOE or the StroWgermechanism included in the finder switch Hills ener gized'oniy once, thereby to cause the carriage of the Strowger mechanism to bemoved inthe rertioal direction, only one stem-jet which: time the controllwiper carried thereby engages the contact'lti' in the row of contacts Ittin the conwith, CHO, the wiper 102v and associated contact 105 of the rotary switch "I, C143, RA133 and the back contact associated therewith, the upper winding of R100, RA145, and the winding of R100 to battery. During the pulsing of the vertical magnet MI of the Strowger mechanism included in the finder switch "I, the relay R155 does not operate due to its slow-to-operate characteristic and to the fact that the "circuit for energizing the lower winding thereof is only intermittently completed, at RA152 and WA152.

When energized over the above-traced circuit the relay R150 remains operated, and the relay R130 partially operates to close .its X contacts associated with its armature RA133', thereby to complete a, holding circuit for energizing the lower winding of R130, this circuit extending from ground, at RAI, by way of M135, and the lower winding of R130 to battery. when this holding circuit is completed, the relay R150 completely operates to interrupt, at RA132, the origi nal circuit for energizing the relay R140, and interrupts, at RA133 and the back contact associated therewith, the circuit for energizing the re- I lay R160, thereby to cause the latter relay to restore. Also the relay R130 prepares, at RA":

and the front contact associated therewith, a circuit traced hereinafter for energizing the upper winding of the switching relay RI80. Further the relay R130 interrupts, at RA13I and the back contact associated therewith, a point in the circuit for energizing the vertical magnet MI05 of the Strowger mechanism included in the finder switch IOI, thereby to prevent further vertical movement of the carriage 0! this Strowger mechanism, and completes, at RA13I and the front contact associated therewith, a circuit for energizing the rotary magnet MI 06 of the Strowger mechanism included in the finder switch IOI subsequent to the restoration of the relay R150,

I the latter circuit extending from ground, at

RA150, by way of RAT, RA16I, RA13I' and the front contact associated therewith, CHI, RAI92, RAIN and the back contact associated therewith, andv the winding of MI00 to battery. Also the relay R130 completes, at RA133', a circuit for energizin'gthe relay R135, this circuit extending from ground, at RA15 I by way of M133, and the windingof R135 to battery. Finally, the relay R130 interrupts, at RA15I, a point in the circuit for energizing the lower winding of the relay R155. When energized over the above-traced circuit the relay R135 operates to set its weighted armature WA135 into vibration, thereby to complete intermittently, at RA135, a circuit for energizing the upper winding of the relay R155, this circuit extending from ground, at RA1I5, by way 4 of WA150, and the upper winding of R155 to battery. As the field produced by the upper winding of the relay R155 is in opposition to that originally produced by the lower winding thereof, and thefacts that the relay R155 is of the slow-tooperate type and the circuit for energizing the upper winding thereof is only intermittently completed, at RA135 and WA105, operation of this relay is further delayed.

when the rotary magnet MI06 of the Strowger extending between the finder switch IM and the mechanism included in the finder switch it! is energized over the previously traced circuit, it operates to rotate the carriage thereof one step in the radial direction, and to complete, at MAI06, a circuit for energizing the relay R160, this circuit extending from ground, at MAI00, by way of CH5, and the winding of R150 to battery. The relay R then operates to interrupt, at RA16I, the circuit for energizing the rotary magnet MI 06, thereby to cause the rotary magnet MI05 to re-' store and interrupt, at MAIOG, the circuit for 'energizing the relay R150. The relayR100 then restores to complete, at RA15 I the circuit for energizing the rotary magnet MI06, thereby to cause the rotary magnet MI00 to operate and rotate the carriage of the Strowger mechanism included in the finder switch IOI a further step in the radial direction, and to complete, at MAI 06, the circuit for energizing the relay R100. The rotary magnet MI05 and the relay R160 continue to interact, as described above, thereby to cause the carriage of the Strowger mechanism included in the finder switch IN to be rotated stepby step in the rotary direction until the wipers carried by the carriage thereof engage the contacts in the contact bank I02 of the Strowger mechanism terminating the calling subscriber line II5.

As previously noted the relay R155 is of the slowto-operate type and does not operate during the pulsing of the rotary magnet'MI06.

When they wipers carried by the carriage of the Strowger mechanism included in the finder switch "I engage-the contacts in the contact bank I02 thereof terminating the calling subscriber line II5, a circuit is completed for energizing the upper winding of the switching relay RI 80, this circuit extending from ground, RA133 and the front contact associated the with, by way of C143, the wiper 102 and associated contact 105 of the rotary switch 10I, CHO, the upper winding of RI00, the control conductor CI20, the wiper carried by the carriage of the Strowger mechanism terminating this control conductor, the contact in the contact bank I02 terminating the control conductor CH8 of the calling subscriber line II5, CHO, RAI51, RAISI, and the winding of RI 50 to battery. When energized over the above-traced circuit the relay RI80 operates to connect, at RAIBI andat RAI82, the conductors CI and CI25, respectively, to the conductors CI2I and CI22 of the trunk line I20 connector switch 200, thereby to connect the calling subscriber line II5 through to the connector switch 200, and to interrupt, at RAIN and the back "X' contact associated therewith, a point in the circuit for energizing the rotary magnet MI" in the Strowger mechanism included in the finder switch IOI, thereby to prevent i'm-ther operation of the rotary magnet MI. Also the relay RI00 completes, at RAIN and the front contact associated therewith, a holding circuit for energizing the lower winding thereof in series with the winding of the rotary magnet MI00, this circuit extending from the grounded control conductor CI23 by way of the lower winding of Rl00, RAIN andthe front contact associated therewith, and the winding of the rotary magnet MI05 to battery. when the rotary magnet MI05 is energized over the abovetracedcircuit it does not operate due to the high series resistance of the lower winding of the re- When direct ground,'as applied to the control conductor CH3, is appliedto the control conthe grounded control conductor CIZB, CIII,

RAI51, RAI5I, and the winding of RI60 to battery. When energized over the above-traced circuit the cut-ofi relay RI60 operates to complete. at RAIBI, a holding circuit for itself extending from the grounded control conductor CH8 by way of RAIGI, and the winding of RIGO to battery. Also the cut-off relay RI60 interrupts, at RAI62 and at RAI63, points in the bridge path for energizing the line relay RIBS, thereby to free the subscriber line H5 of impedance elements, and to cause the line relay RISE to restore. Further the cut-off relay RI60 completes,

' at RAI64 and the front contact associated therepaystation type, this connection extending from the paystation tone lead CI41-by way of the condenser I48, RAI64 and the front contact associated therewith, and RAIBI to the control conductor CI I8 of the subscriber line II5. In the event the subscriber substation A is of the paystation type, paystation tone current is pro- J'ectedrover the control conductor CH! of the subscriber line 5 by way of the operated .finder switch IOI into the associated connector switch 200 for a purpose more fully described subsequently. Finally, the cut-oil relay RI60 completes, at RAI65 and the front contact associated therewith, an'obvious circuit for energizing the lockout relay RI50. Upon restoring, the line relay RI55 interrupts, at RAI58, a point in the path for applying ground potential to the start lead CI31 extending into the distributor 100, and in the path for applying marking ground potential to the conductor CI35' terminated bythe this path extending from ground, at RA15I, by way of RA141, the winding of R140, RA1I I, the self-interrupting contacts MA10I of the rotary magnet M10I, RA"! and the front contact as-' sociated therewith, C1, the wiper 103 and associated' contact 101 of the rotary switch 10I, CI43, RAI93 and the front contact associated therewith, RAIIS, RAI92, CI4I RA13I and the front contact associated therewith, RA16I, and RA144 to ground, at RA158. When the relay R140 is thusshort-circuited it restores to interrupt, at RA141, a point in its holding circuit; and when the rotary magnet M10! is energized over the above-traced circuit it operates to interrupt, at MA10I, a point in the original circuit for energizing the relay R140.

At this time, if no other calls have been initiated in the group of subscriber lines including the subscriber line H5 when ground potential is moved from the startlead CI31, the start relay R120 restores. Upon restoring, the relay R120 interrupts, at RA120, a further point in the original circuit for energizing the relay R140,

and interrupts, at RA12I, apoint in the prepared circuit for illuminating the signal lamp 122. Upon restoring, the relay R140 interrupts, at RA143, the circuit for energizing the relay RI90. However, the relay RI90, being of the slow-to-release type, does not restore imme-.-

diately. Also, upon restoring, the relay R140 circuit for energizing the rotary magnet M10I of contact I04 in the contact 'bank I04 of the Strowger mechanism included in the finder switch l0l. When thus energized, the look-out relay RI operates to interrupt, at RAI53 and the back contact associated therewith, a furtherpoint in the paths for applying ground potential to-the start lead CI31 and the conductor CI35'. Also, upon restoring, the relay RI 55 completes, at RAISE and the back contact associated therewith, a path-for applying ground potential from the control conductor CI I8 of the subscriber line II5 extending to the finder switch IOI to the control conductor CI I9 of the subscriber line I I5 extending to the contact banks of the Strowger mechanisms included in the connector switches of the links having access to the subscriber line I I5, thereby to mark this subscriber line as busy. The last-mentioned path extends from the grounded control conductor CI I3 by way of RAIGI and RAI56 and the back contact associated therewith, to the control conductor CH9.

Furthermore, upon operating, the relay RI00 completes, at RAI85, a circuit for energizing the rotary magnet M10I of the rotary switch "I in' the rotary switch 10I,'and prepares, at RAI42 and the back contact associated therewith, an

'altemative circuit traced hereinafter for energizing the rotary magnet M10I of the rotary switch "I. Further, the relay R140 interrupts, at RA146, the circuit for energizing the relay R150, and interrupts, at RA14I, the holding circuit for the switch-over relay R1l0. At this time the relay R1I0 remains operated only in the event there is an idle link in the first group of links. The relay R150 then restores to interrupt, at RA152 and WA152, a further point in the circuit for energizing the lower winding of the relay R155, and interrupts, at RA15I, the circuit for energizing the-relay R135, and the holding circuit for energizing the-lower winding interrupting contacts MA10I, a point in the original circuit for energizing the relay R140.

' The test relay R130 then restores, thereby to in- 103 and associated contact 101 of the rotary switch 10I, C14I,'RA142 and the front contact terrupt, at'RA133 and the front contact associated therewith, the path for applying ground potential to the test conductor C143, and to prepare, at RA133 and the back contact associated therewith, the original circuit for energizing the upper winding of the relay R130. Also, upon restoring, the relay R interrupts, at RA'I3I and the front contact associated therewith, a further point in the circuit for energizing the rotary magnet MI06 of the Strowger mechanism included in the finder switch IOI,

contact associated therewith, the path for-applying multiple ground potential to the control conductor CW3, ground potential being applied to the control conductor Cl23 at this time. in the connector switch 290 associated with the finder switch Mi in a manner more fully described sub- RIM prepares, at RAl94 and the back contact associated therewith, a point in a circuit traced hereinafter for energizing the release magnet MW! of the Strowger mechanism included in 'thefinder switch l0l, this circuit beinginterrupted at this time, at RAlllB of the operated relay R180, and completes, at RAISQ and the back-contact associated therewith, a pathlfor applying ground potential to the guard conductor C843,. this path extending from ground at the switch spring H0 of the vertical off-normal springs I08 associated with the St'rowger mechanism included in the finder switch ID! by way 'sequently. Finally, .upon restoring, the. relay of the switch spring H0 and RAI93 and the" back contact associated therewith, to the guard conductor Cit-3. This application of ground potential to'the guard conductor :Cl43 marks the finder switch l0l of the link as busy to the distributor 100. i

At this time the wipers 102, 103, 1M, and of the rotary switch 10l in the distributor 100 engage the. control conductors extending to the finder switch of the next link in the first group aasaefos rotary switch ldi engage a cont'act set therein terminating the control conductors of a finder switch of an idle link in the first group oflinks, at which time the circuit for energizing the. rotary magnet Midi. is interrupted due to the absence of ground potential upon the guard conductorof the finder switch of this idl link. At this time the distributor 108 is completely released and .in condition to assign the selected idle link in the first group of links to the use of a calling line when the next'call is initiated on a line in the first group of lines. served by the distributor ltd.

- Should a call be initiated on a line in the first group or lines prior to the operation of thev distributor W0 to select an idle link in the first I group of links, the start'relay R129 operates, as previously explained. However, operation of the relay Rltt at this time-is ineiiective to cause the relay Ride to operate as the latterrelay remains Y short-circuited due to the presence of ground upon the guard conductor .CMl, as previously noted, so long as the wipers of the rotary switch m in the distributor 100 encounter contacts thereof terminating control conductors of finder switches associated-with busy links in the first group of links.

-As previouslynoted, upon the operation of the switching relay Ri$0 incident to the seizure of the calling subscriber line "lit by the finder switch ldi oi the link 00,'the relay R is short-circuited and restores. Upon restoring, the relay Rllli interrupts, at RAHi, the holding circult for the switch-over relay R110, which latter relay is retained in its operated position only in the event. that there are other idle links in the first group of links; due to the fact that ground potential is applied to, the all trunks busy conductor CH2 only in the event there are other idle links in the first group of links. At this time,

7 in the event all of the links in the first group oi of links, and if this link is busy, ground potential appears upon the guard conductor thereof, thereby to complete a path for applying ground potential to the guard conductor CHI. This application of ground potential to the guard conductor C1 completes a circuit for energizing the rotary magnet mm of the rotary switch 10l, this circuit extending from the groundedguard conductor CHI, by way of RA142 and the back contact associated therewith, RAHI, the self-interrupting contacts MA10'I of the rotary links are busy, the relay'RlHI restores. Upon restoring, the relay RElfl interrupts, at RA1I3 and the front contact associated therewith, the. connection between the start lead CW1 and the start relay R1i0, thereby to prevent the distributor 100 from being started into operation magnet M10l, and the winding of M10! tov battery. Also, this application of ground poten-.-

tlal to the guard conductor 014i prepares a point in a path for short-circuiting the winding. of the relay R140, thereby to prevent the latter relay from operating upon operation of the relay R120 incident to the initiation of another call in the'group. of subscriber lines servedby the distributor 100 prior to the operation or the distributor 100 to select an idle link in the first .group or links for the use or a calling line; When energized over the above-traced circuit the rotary magnet M10| operates to move the wipers noted otthe rotary switch 10l into engagement with the contacts thereof terminating the con trol conductor of the next link in the first group of links. In the event this link is alsofibusy, ground potential appears upon the guard condoctor thereof, thereby to cause the rotary magnet M101 to again operate, as described above. The rotarymagnet M101 continues to operate, as described above, until the wipers noted 01 when the next call in the group or lines served thereby is initiated on one of these lines. Also. upon reatoring; the relay R1l0 connects, at RAHS and the. back contact associated therewith, the start lead Clllto the conductor C extending to the distributor individually associated; with the second group of lines, thereby rendering the last-mentioned distributor effective to assign an idle link in the second group of links to the use of a calling line in the first group of lines while all 01' the links in the first group 0! links are busy; The operation of the distributor individually-associated with the second group of lines to assign a. previously selected 'idle-link'in the second group 01' links to the use of a calling line in the first group or lines is otherbyto prevent unnecessary operation 'of'the rotary ma net M1" when all of the linksin the first group of links are busy.

In the foregoing description of the operation of the finder switch Ill ofthe link 80 it was assumed that the carriage of; the Strowger mechmism included therein was rotated step by step the finder'switch thereby to arrest further rotary movement of the carriage of this Strowger mechanism, and to connect the calling subscriber line throughto the connector switch 200, as previously noted. However, should the wipers carried by the carriage of this Strowger mechanism fail to encounter the contact in the contact bank !02 terminating the control conductor CH8 of the calling subscriber line H5 or to make imperfect contact therewith such that the switching relay Rl80 fails to operate, the rotary magnet M!06 of this Strowger mechanism operates intermittently until the carriage thereof is moved into its eleventh radial position. When the carriage of this Strowger mechanism is rotated into the eleventh radial position the rotary switch springs I09 are moved into engagement, thereby to complete a path for applying ground potential to the ground conductor CH3, this path extending from ground at the rotary switch springs 109 by way of RA|93 and the front contact associated therewith to the guard conductor CH3.

This application of ground potential to the guard conductor C143 completes the previously traced circuit for energizing the rotary magnet M10! of the rotary switch 1i in the distributor 1019, thereby to cause the distributor 100 to operate to select the next idle link in the first group of links for the use of the calling subscriber line 0nd group of links, this circuit extending from the grounded all trunks busy conductor C183 by way of the switch 180, RA159, and the'winding of R150 to battery. Also the relay R155 completes, at RA151, a path for applying round potential to the guard conductor CHI, this path extending from ground, at RA15I, by way of 1 RA141 and RA151 to the guard conductor C1. This application of ground potential to the guard conductor C14! completes the previously traced circuit for energizing the rotarymagnet M10! of the rotary switch 10! in the distributor 100, and completes the previously traced path for short-circuiting the winding of the relay R140. The relay R140 then restores and interrupts, at RA142 and the front contact associated therewith, a point in the circuit for energizing the rotary magnet M10! of the rotary switch 10!, thereby to cause the rotary magnet M10! to restore and advance the wipers noted of the rotary switch 10! one step and into engagement with the contacts terminating the control conductors of the finder switch in the nextlink in the first group of links. Also the relay R140 interrupts, at RAHI, the holding circuit of the re-i lay R1!0; and the operated relay R155 interrupts, at RA156, a point in the circuit for energizing the relay R110 by way of the all trunks busy conductor OM12, thereby to cause'the relay R1! to restore. Upon restoring, the relay R1!0 interrupts, at RAH a point in the original circuit for energizing the relay R140 and a point H5, in'the manner previously explained. Thus it will be apparent that the distributor is so connected and arranged that a second idle'link in the first group of links is automatically selected for the use of a calling line in the event that the finder switch of a first selected link in the first group of links fails to find the calling line.

Also it is noted that an arrangement is incorporated in the distributor 1th for locking this distributor. out of service in the event that it fails to operate properly to cause the finder switch of an idle link in the first group of links selected,

thereby to seize a calling subscriber line. Forexample, should either the vertical magnet Miil5 or the rotary magnet Mitt of the Strowger mechanism included in the finder switch mi of the link 80 fail to cause the relay Rita to transmit operating pulses to either one of these mag-- lay R160 to transmit pulses thereto; the operated relay R150 causes the circuit for energizing the lower winding of the relay R155 to be energized a time interval sumciently long to cause the relay R155 to operate. In the event that the rotary gizing the relay R150 is completed by way of the l all trunks busy conductorCliit of the distributor in this circuit for energizing the rotary magnet M10! of the rotary switch 10! in the distributor 1110. Furthermore, the relay RHil interrupts, at RAlIii and the irontcontact associated therewith, a point in the circuit for energizing the start relay R by way of the start lead CH1, and completes, at RAflitl and the back contact associated therewith, a connection between the start lead C131 and the conductor C165 extending to the distributor associated with the second group of links. It is noted that the circuit for enerassociated with the second group of links and that the operated relay R retains completed the circuit for energizing the lower winding of the relay RlSd. In turn the operated relay R remagnet MI06 fails to operate or to cause the' relay R to transmit pulses thereto, the operated relay R135 causes the circuit for energizing the upper winding of the relay R155 to be energized a time interval sufficiently long to cause the relay R155 to operate. Upon operating, the relayR155 completes, at R'A159, a circuit for energizing the relay R150 by way of the all trunks busy conductor C163 extending to the distributor individually associated with the m tains the circuit for energizing the relay R150 completed at M159. Accordingly, the relays Rlbb and R155 remain in operated positions until the circuit for energizing the relay R51!) is interrupted by manually operating the switch to its open position. Thus the distributor 100 associated with the first group of links is permanently locked out of service until the switch 100 is manually operated. I

Before continuing with the operation of the connector switch 200 associated with the finder switch in! in the link 60, it is noted that the finder switches of the links in the first group of links may be tested automatically and sequentially by operating the, test switch 182 to its closed position. When the test switch 132 is thus operated a circuit is completed for energizing the start relay R120, this circuit extending from ground, at the test switch 182, by way of the resistor 18!, the start lead Cl31, RA1!3 and the the distributor no to assign the previously select-.

ed link to the use of a calling line.

Assuming that the illustrated link 50 is the link previously in the vertical direction.

.guard conductor CH3.

.ner similar to that described above. eration of the distributor I will continue as selected by the distributor 100 to the use of the calling 'line, the distributor 100' then operates to cause the vertical magnet MW!) of the Strowger mechanism included in the finder switch i0l to operate intermittently, thereby to move the carriage of this Strowger mechanism Assuming that no legitimate call is initiated on a line in the first group of lines during the time interval the finder switches of the links in the first group of links are being tested, the carriage of the Strowger mechanism included in the finder switch It! is moved vertically to the tenth level wherein the previously traced circuit for energizing the upper. winding of the relay R130 is completed due to the fact that the tenth contact in the row of contacts I04 in the contact bank of this Strowger mechanism is permanently grounded. The relay R130 then operates, as previously explained, thereby to cause the rotary magnet Mi06 to be intermittently energized in order to drive the carriage of the Strowger mechanism included in the finder switch |0l step by step in a rotary direction until this carriage is moved into the eleventh radial position. When the carriage of the Strowger mechanism included in the finder switch I0! is moved into the eleventh radial position, the rotary springs I09 are closed, thereby to cause ground potential to be applied to the This application of ground potential to the guard conductor CH3 causes the rotary magnet M10| of the rotary switch 10! to be energized, thereby to drive the wipers noted of, the rotary switch 10! one step and into engagement with the contacts terminating the control conductors of the finder switch in the next idle link. The finder switch of the next idle link is then caused to operate in a man- This oplinks in the first group of links are being tested,

the wiper carried by the carriage of the Strowger mechanism included in an operating one of the finder switches will engage the marked contact in the row of contacts corresponding to the row of contacts I04 in the contact bank of this Strowger mechanism prior to the movement of the carriage of this Strowger mechanism in the vertical direction to the tenth level, thereby to cause this operating'finder switch to seize the calling line. After this finder switch seizes the calling line, the distributor I00 continues to operate as previously described to test the remainder of the finder switches of the idle links in the first group of links.

Continuing now with the operation of the connector switch 200 to extend the call from the subscriber substation A to the subscriber substation C, when the relay R190 in the finder switch I0l operates to complete the previously traced path for applying ground potential to the a control conductor CI23, a circuit for operating across the line conductors CH6 and Cl ll of the calling subscriber line 5 subsequent to ,the operation of the finder switch IM to seize the calling subscriber line H5.

After the finder switch l0! seizes the calling subscriber line H5, and theswitching relay RIBD operates to connect the calling subscriber line H5 to the trunk line I20, a loop circuit is completed for energizing the relay R260, this circuit extending from ground, at RA2'II, by way of RA2I2, the lower winding of R260; R0256, RA255, R0246, RA245, C203, RA2I2, C122, RAI82, Cl25, the wiper and contact in the Strowger mechanism included in the'finder switch ml, the

bridge at the substation A between the line conductors C! H and CH6 of the subscriber line H 5, CH6, the contact and wiper of the Strowger mechanism included in the finder switch MI, 0124, RAIN, Ci2l, RA2l I,.C202, RA242, R0243, RA252, RC253, and the upper. winding of R260 to battery. When energized over the abovetraced circuit the relay R260 operates tocomplete, at RA26| and the front contact associated therewith, a circuit for energizing the hold relay R265, this circuit extending from ground, at RA24I, by way of RA26I and the front contact associated therewith, and the winding of R265 to battery. When energized over the abovetraced circuit the relay R265 operates to complete, at RA265 and the front contact associated therewith, a path for applying multiple ground potential to the control conductor Cl23, this path extending from; ground, at RC236, by way of RA235, C239, and RA265 and the front contact associated therewith, to C123. It is noted that the relay R265 operates to apply multiple ground potential'to the control conductor Cl23 prior to the restoration of the relay RI in the finder switch l0l due to the slow-to-release characteristic of the latter relay. Also, upon operating, the relay R265 prepares, at RA269, a circuit for impulsing the control magnets of the Strowger mechanism and the minor switch 325 included in the connector switch 200, in a manner more fully described subsequently. Also, it is noted that the ground potential connected to RA21I is connected thereto by way of a dial tone conductor.

Thus it will be apparent that dial tone current is returned to the substation A over the previouslytraced loop circuit extending thereto in order to actuate the receiver of the telephone instrument thereat, thereby to indicate to the subscriber at the substation'A that a link has been seized and that the first digit of the directory number of the called subscriber line may be dialed. Also the relay R265 completes, at RA266, an obvious circuit for energizing the relay R225, which latter relay operates to apply, at RA226, ground potential to the time start lead C229 for a purpose more fully described subsequently.

The subscriber at the substation A then dials the first digit of the directory number of the called subscriber line at the dial mechanism thereat, thereby to transmit a first series of impulses by wayof the subscriber loop circuit to the line relay R260. The relay R260 follows the dialed impulses in the usual manner, restoring eachtimethe loop circuit is interrupted, and operating each time the loop circuit is completed. Each time the relay R260 restores it interrupts, at RA26I and the front contact associated therewith; the energizing circuit of the relay R265, and completes, at RA26i and the back contact associated therewith, a circuit for energizing in multiple the lower winding of the relay R210 and the vertical magnet M26l of the Strowger mechanism included in the connector switch 200. The lastmentioned circuit extends from ground, at RA241, by way of RA26I and the back contact associated -therewith,and RA253 to RA214 and the front contact associated therewith, one branch of this circuit extending from the front contact associated with RA214 by way of the lower winding of R210 to battery, and the other branch extending from the front contact associated with RA214 by way of the winding of the vertical magnet M20I to battery. The relays R265 and R210 are of the slow-to-release type. Thus, these relays remain operated during impulsing. Each time the vertical magnet M20I is energized the carriage of the Strowger mecha-' nism included in the connector switch 200 is moved one step in the vertical direction. When the carriage. of this- Strowger mechanism is moved away from its normal position one step in the vertical direction, the vertical off-normal springs 209 and 325 are actuated. The vertical off-normal springs 203 are actuated to interrupt the circuit for energizing the upper winding of the relay R216, and. the vertical off-normal springs 3E5 are actuated to prepare a point in the circuit for energizing the release magnet W133i of this Strowger mechanism. At the conclusion of the first digit dialed the relay R263 reoperates, thereby to interrupt, at RA26I and the back contact associated therewith, the previously traced circuit for energizing in multiple the lower winding of the relayRfld, and the winding of the vertical magnet Midi, When this circuit is interrupted further operation of the vertical magnet M20! is arrested, thereby The subscriber at the substation A then dials the second digit of the directory number of the called subscriber line at the dial mechanism thereat, thereby to transmit a second series of impulses by way of the subscriber loop circuit to the line relay R260.v The line relay R260 follows the dialed impulses, as previously explained. Each time the relay R260 operates, it completes, at RA26| and the front contact associated therewith, the previously traced circuit for energizing the relay R265. Each time the relay R260 restores, it completes, at RA26| and the back contact associated therewith, the circuit for energizing in multiple the relay R280 and the rotary magnet M346, this circuit extending from ground, at RA241, by way of RA26I and the back contact associated therewith, RA269, RA214 and the back to arrest the carriage of the Strowger mechanism included in the connector switch 263 in a vertical position corresponding to the first digit dialed and to the level in the contact bank 300 of this Strowger mechanism in which are disposed the contacts terminating the conductors of the called subscriber line 3i5 extending to the substation C. Shortly after this circuit is interrupted the relay R210, being of the slow-to-release type. restores to interrupt, at RA21I and RA212, the circuit for returning dial tone current to the substation A by way of the loop circuit, and tocomplete, at RA212 and R0213, an alternative circuit for energizing the relay R260 by way of the previously traced loop circuit. This alternative circuit for energizing the relay R260 extends from ground, at RA26B, by way of R0213 and RA212 to the lower winding of R260, the extension of this circuit by way of the loop circuit to battery associated with one terminal of the upper winding of R260 being the same asthat previously traced. Also, upon restoring, the relay R210prepares, at RA214 and the back contact associated therewith, a point in a circuit traced hereinafter for energizing in multiple the relay R280 and the rotary magnet M346 of the Strowger mechanism included in the connector switch 200.

contact associated therewith, C286, and RA399' to RA316, one branch of this circuit extending from RA313 by way of RA311, C285, and the winding of R280 to battery, and the other branch of this circuit extending from RA318 by way of RA350 and the back contact associated therewith, C238, and the winding of M346 to battery. Due to the slow-to-release characteristics of the relays R280 and R265, these relays do not restore during impulsing. Each time the rotary magnet M346 is energized the carriage of the Strowger mechanism included in the connector switch 200 is moved one step in the rotary direction, At the conclusion of the second digit dialed the carriage of the Strowger mechanism included in the connector switch 200 occupies a radial position corresponding to the second digit dialed, and causes thewipers carried thereby to engage the contacts Y in the contact bank 306 of thi Strowger mechtery. When energized over the above-traced circuit the relay R335 operates to complete, at RA348', a path for short-circuiting the relay R356, this path extending from the grounded conductor C2371, by way of RA348, RC353, RA35 I. the winding of R356, and RA363 to the grounded control conductor (H23. At the conclusion of the second digit dialed the line relay R260 reoperates to interrupt, at RAM! and the back contact associated therewith, the previously traced circuit for energizing in multiple the relay R260 and the rotary magnet M3t6, thereby to arrest further operation of the rotary magnet M346, and, consequently, further movement in a rotary direction of the carriage of the Strowger mechanism included in the connector switch 200.

Shortly thereafter the relay R260 restores to interrupt, at RA232 and the front contact associated therewith, the previously traced circuit for energizing the relay R345 and the previously traced path for short-circuiting the relay R350. The relay R350 is then energized in series with the relay R345 byway of a circuit extending from the grounded control conductor (H23 by way of RA363, the winding of R350, RA35I, R0353, RA348, and the winding of R345 to battery. When energized over the above-traced circuit the relay R350 operates to complete, at RA35I and RA352, a holding circuit for itself extending from the grounded control conductor Cl23 by way of RA363, the winding of R350, RA35I, RA352, and

the resistor 350 to battery. Also the relay R350 interrupts, at RA35| and R0353, the original circuit for energizing in series the relays R350 and R345, thereby to cause the relay R345 to restore shortly thereafter. Further the relay R350 prepares, at RA350 and the front contact associated therewith, a circuit for energizing in multiple the relay R280, and the rotary magnet M345 of the minor switch 325.-

At this time the subscriber line 3I5 has been seized by the connector switch 200. However, the subscriber line 315 is not tested in order to determine the idle or busy condition thereof until after the third and last directory digit of the tory digit being effective to cause a predetermined type of ringing current to be projected over the subscriber line 3l5v in the event this subscriber line is idle, in a manner more fully described subsequently. The subscriber at the substation A then dials at the dial mechanism thereat, the third digit of the directory number of the called subscriber substation C, thereby to transmit a third series of impulses by Way of the subscriber loop circuit to the line relay R260. The line relay R260 follows the dialed impulses, as previously explained. Each time the relay R260 operates it completes, at RA26| and the front contact associated therewith, the previously traced circuit for energizing the relay R265, and each time the relay R260 restores it completes, at RA26l and the back contact associated therewith, a circuit for energizing in multiple the relay R280 and the rotary magnet M345 of the minor switch 325, this latter circuit extending from ground at RA241, by way of RA26l and the back contact associated therewith, RA269, RA214 and the back contact associated therewith, C286, and RA3S9' to RA313, one branch of this circuit extending from RA318 by way of RA311, C285, and the winding of R280 to battery, and the other branch of this circuit extending from RA318 by way of RA350 and the front contact associated therewith, C605, and the winding of the rotary magnet M345 to battery. When energized over the above-traced circuit the relay R200 operates to complete, at RA282 and the front contact associated therewith, the previously traced circuit for energizing the relay R345, and interrupts, at RA20I, a point in a test circuit traced hereinafter including the control wiper 303 carried by the carriage of the Strowger mechanism. When energized over the above-traced circuit the relay R345 operates to interrupt, at RA345, a point in a busy tone circuit traced hereinafter, and prepares, at RA348 and RA349, a point in the previously mentioned test circuit including the control wiper 303 carried by the carriage of the Strowger mechanism,

and prepares, at RA346, a point in a test circuit traced hereinafter including the control wiper 304 carried by the carriage of the Strowger mechanism. At the conclusion of the third digit dialed the wipers 321, 33l and 335 of the rotary switches 326, 330 and 334, respectively, engage the contacts in their respective contact banks normal springs 339 associated therewith are actuated. When the off-normal springs 339 are actuated the switch springs 340 and 34i are moved into disengagement, thereby to interrupt a point in a circuit traced hereinafter for energizing the release magnet M344 associated with the Strowger mechanism included in the connector switch 200; and the switch springs 3M and 342 are moved into engagement, thereby to prepare a circuit traced hereinafter for energizing the release magnet M343 of the minor switch 325.

Shortly after the conclusion of the third digit dialed the relay R280, being of the slow-to-release type, restores to complete, at RA28I, the previously mentioned test circuit for determining the idle or busy condition of the called subscriber line 315. More particularly, this test circuit includes the test relay R310 and the control wiper 303 carried by the carriage of the Strowger mechanism included in the connectorswitch 200. At this time the control wiper 303 engages the contact 300 in the contact bank 300 of this Strowger mechanism, and the previously mentioned test circuit extends from the control conductor C3l6 of the called subscriber line 3l5 by way of the contact 303, the control wiper 303, G820, the multipled contacts in the contact bank 331 of the rotary switch 334, the wiper 335 thereof, the conductor 336, C241, RA26I, C204, RA348, RA349, and the winding of R310 to battery,

The subsequent operation of the connector switch 200 depends upon whether the called subscriber line 3l5 is idle or busy. Assuming that the called subscriber line is busy, ground potential appears upon the control conductor C3l6 thereof which is derived by way of the line, circuit associated therewith, thereby to cause the test relay R310 to be energized over the above-traced test circuit. When thus energized, the relay R310 operates to prepare, at RA312 and the front contactassociated therewith, a holding circuit for itself, which holding circuit is completed when the relay R345 restores shortly after the restoration of the relay R230, and extends, when completed, from the grounded control conductor Cl23 by way of RA312 and the front contact associated therewith, R0349, RA340, and the winding of R310 to battery. Also, the relay R310 interrupts, at RA311, a further point in the circuit for energizing the relay R280, and interrupts, at RA318, a further point in the circuit for energizing the rotary magnet M345 of the minor switch 325. Further, the relay R310 completes, at RA314, subsequent to the restoration of the relay R345, a circuit for returning busy tone current over the loop circuit extending to'the calling subscriber substation A. The circuit for returning busy tone current over the loop circuit extending to the calling substation A extends from the ungrounded terminal of a busy tone transformer winding by way of the busy tone lead C6l9, RA391, RA314,

the condenser 345, RA345, C230, the condenser R260, RC256, RA255, R0246, RA245, C203, and

RA2I2 to the line conductor Cl22, the connection between the line conductors Cl2l and CI22 of the trunk line I20 including the loop circuit extending to the calling subscriber substation A being the same as that previously traced. When busy tone current is thus returned over the loop circuit to the calling-subscriber substation A, the

receiver of the telephone instrument thereat is actuated, thereby to indicate to the subscriber thereat that the desired connection cannot immediately be had due to .the busy condition of the called subscriber line H5. The subscriber at the-calling substation A then releases the operated link 50 including the finder switch IM and the connector switch 200, and the line circuitl by placing the receiver of the telephone instrument at the substation A upon its hook. The exact manner in which these operated pieces oi apparatus are released is described in detail hereinafter.

Assuming that the called subscriber line M is idle, battery potential appears upon the control conductor C3|5 thereof which is derived by way of the line circuit associated therewith, thereby to cause the test relay R310 to be short-circuited by wayof the previously traced test circuit.

Shortly thereafter the relay R345 restores, as previously noted, thereby to complete, at RA300 and RC348, a circuit for energizing the upper winding of the switching relay R395. This circuit extends from ground, at RA26I, byway of C299, RA315, C8ll, the upper winding of R395, C8 l8, RA375 and the back contact associated therewith, R0349, RA348, C234, RA28I, C2", the conductor 335 in the rotary switch 334, the

wiper 335, a contact in the associated multipied contact bank 331, C820, C900, the control wiper 303, and the contact 309 in the contact bank 300 of the Strowger mechanism included in the connector switch 200, to battery potential appearing on the control conductor C3; of the subscriber line 345. When energized over the above-traced circuit the relay R395 operates to complete, at RA398, a holding circuit for energizing the lower winding thereof, this circuit extending from ground, at RA258, by way 01' C233, RA399, and the lower winding of R395 to battery. 'Also, the relay R395 connects the conductors CBII and CH5, at RA395 and RA395', respectively, to the conductors 029i and C293. When the conductors C8H and Ciilfi are respectively connected to the conductors C29l and C293, battery and ground potentials are respectively extended to the wipers 30! and 302 carried by the carriage in the Strowger mechanism included in the connector switch 200. The path for extending battery potential to the wiper 30l extends from battery at the u'pper winding of the ring cut-oil relay R360 by way of the upper winding of R360, C8l2, RA39I and the back contact asso- 1 ciated with the called subscriber line 3|5, and marks the subscriber line 3| 5 as a busy line to the connector switches of the links having access thereto. Further, the relay R395 completes, at RA399, a path for energizing the relay R300 by way of the ring pick up lead C822 in the event code ringing is employed in the system, as is more fully explained subsequently. This path extends from ground potential appearing upon thering pick-up lead C822 at a predetermined time by way of the X" wiringillustrated, RA399, R0384, RA383, RA354, and the winding of R380 to battery. Further, the relay R395 completes, at RA399, a path for energizing the relay R390 by wayof the lead C82l in the event harmonic ringing is employed in the system, as is more fully explained subsequently. This path extends from the grounded lead C82l by way of the "Y wiring illustrated to the front contact associated with RA399 and over the previously traced circuit to battery. Furthermore, the relay R395 interrupts, at RA399', a further point in the circuit for energizing the rotary magnet M345 of the minor switch 325, thereby to arrest further operation thereof, and connects, at RA396', the lower winding of the ring control relay R390 to the even contacts in the rotary switch 325 of the minor switch 325 for a purpose more fully explained subsequently. This connection extends from battery at the lower winding of the relay R390 by way of the lower winding of R390, MAME, RA394, RC394, RA396, and C803 to the multiple connected even contacts in the rotary witch 326. Finally, the relay R395. prepares, at RA39I' and the front contact associated therewith, a point in a holding circuit ing of the ring control relay R390.

. code ringing current comprisingdifferent comconductors respectively terminating at the ten ciated therewith, C0l0, RAI and the back contact associated therewith, CBH, RA395, and C29! to the wiper 30l The path for extending ground potential to the wiper 302 extends from ground, at RA30I and the back contact associated therewith, by way of RA39I' and the back contact associated therewith, C0, RA362 and the back contact associated therewith, C9i5, RA395'. and C293 to the wiper 302. Also,-the

relay R395 connects, at RA398 'and the front contact associated therewith, direct ground potential to the control wiper 303, this connection extending from ground, at RA395 and the front contact associated therewith, by way of C900 to the control wiper 303. At .this time it is noted that the wipers 30L 302, and 303, respectively, engage the contacts 305, 301, and 309 in the contact. bank 300 of the Strowger mechanism res ectively terminating the conductors C324, C325, and C3l6of the called subscriber line 3l5. This application of direct ground potential to the control wiper 303 completes a path for energizing certain relays in the line circuit asso- The subsequent operation of the connector switch 200 depends upon whether code or harmonic ringing is employed in the system and upon whether the third digit dialed is an odd or even digit. In the event that code ringing is employed in the system, the conductors respectively terminating at the ten contacts in the contact bank 329 ofthe rotary switch 326 of the minor switch 325 are respectively connected to ten difierent codes of a source ofalternating binations of long and short pulses. Inthe event harmonic ringing is employed in the system, the

contacts in the contact bank 329 of this rotary switch 329 are respectively connected to ten difierent frequencies of a source of harmonic ringing current. In the event the third digit dialed is an odd digit the ring control relay R390 is not operated. 0n the other hand, in the event that the third digit dialed is an even digit the' relay R390 is operated. Also, a divided or a bridged ringing circuit may be employed in the system in a manner more fully described subsequently.

Assuming that code ringing is employed in the system and that the third digit dialed is an odd digit (for example, No. 1), a path is comthe contact bank 329 of the rotary switch 326, the wiper 321, the multipled odd contacts in the contact bank 328 of the rotary switch 326, the conductor C802, RA38| and the front contact associated therewith, RA39I' and the back contact associated therewith, C8i4, RA362 and the back contact associated therewith, CH5, RA-395', C293, the wiper 302, and the contact 301 in the contact bank 300, to the line conductor C325 of the subscriber line 3l5. vided ringing circuit is employed in the system, this code ringing current is then conducted from the line conductor C325 of the subscriber line 3l5 by way of a condenser and a ringer at each of a first group of subscriber substations, including the substation C, to ground, thereby to cause the ringers at each of the substations in the first group and connected between the line conduc tor C325 and ground to be actuated in accordance with this code ringing current. The subscriber at the substation C is advised that the substation C is the called substation by the characteristic operation of the ringer thereat. In the event that a bridged ringing circuit is employed in the system this code ringing current is then conducted from the line conductor C325 of the subscriber line 3l5 by way of a condenser and a ringer at each of a group of subscriber substations including the substation C, to the line conductor C324 of the subscriber line 3l5, thereby to cause the ringers at each of the substations in the group and connected between the line conductors C325 and C324 to be actuated in accordance with this code ringing current. The subscriber at the substation C is advised that the substation C is the called substation by the characteristic operation of the ringer thereat. This code ringing current is then conducted from the line conductor C324 of the subscriber line 3l5' by way of the contact 305 in the contact bank 300 of the Strowger mechanism" included in the connector switch 200, the wiper 31, 029i, RA395, C8l I, RA36I and the back contact associated therewith, C8l0, RA39| and the back contact associated therewith, C8l2, and the upper winding of the ring cutofi relay R380 to battery.

Assuming that code ringing is employed in the system and that the third digit dialed is an even digit (for example, No. 2), a path is completed at this time for energizing the lower winding of the ring control relay R390, this path extending from the ungrounded terminal of a grounded generator in the'source of alternating code ringing current by way of the conductor terminating at the second contact in the contact bank 329 of the rotary switch 326, the wiper 321, the multipled even contacts in the contact bank 328 of the rotary switch 326, the conductor C003, RA396', R0394. RA394, MA346, and the lower winding of R390 to battery. When energized over the above-traced circuit the relay R390 operates to complete, at RA393 and RA394, a holding circuit for energizing in series the upper and lower windings thereof, this circuit extending from the grounded control conductor Cl23 by way of the upper winding of R390, RA391' and the front contact associated therewith, RA393. RA394, MA346 and the lower winding of R390 to battery. Further the relay R390 interrupts.

at RA394 and RC394, the original circuit for energizing the lower winding thereof, and completes. at RA39I and the front contact associated therewith, at RA39! and the front contacts associated therewith, and, at RA392,'-a circuitfor projecting coded ringing current from the con- In the event that a di-- ductor terminating at the second contact in the contact bank- 329 of the rotary switch 328 by way of the conductor C29| over the subscriber line conductor C324, this path extending from the ungnounded terminal of the grounded generator in the source of alternating code ringing current by way of the conductor terminating at the second contactin the contact bank 329 of the rotary switch 326, the Wiper 321, the multipled even contacts in the contact bank 328 of the rotary switch 326,.the conductor C803, RA396, RA392, RA38I and the front contact associated therewith, RA39I and the front contact associated therewith, C8l0, RA36I and the back contact associated therewith,, C8l I, RA395, C29l, the wiper SM, and the contact 305 in the contact bank 300 to the line conductorC324 of the subscriber line 3l5. In the event that a divided ringing circuit is employed in the system this-coded ringing current is then conducted from the line conductor C324 of the subscriber line M5 by way of a condenser and a ringer at each of a second group of subscriber substations including the substation C to ground, thereby to cause the ringer at each of the substations in the second group, and connected between the line conductor C324 and ground, to be actuated in accordance with this code ringing current. The subscriber at the substation C is advised that the substation C is the called substation by the characteristic operation of the ringer thereat. In the event that a bridged ringing circuit is employed in the system this code ringing current is then conducted from the line conductor C324 of the subscriber line 3l5 by way of a condenser and a ringer at each of a group of subscriber substations including the substation C to the line conductor C325 of the subscriber line 315, thereby to cause the ringer at each of the substations in this group, and connected between the line conductors C324 and C325, to be actuated in accordance with this code ringing current. 'The subscriber at the substation C is advised that the substation C is the called substation by the characteristic operation of the ringer thereat. .This code ringing current is then conducted from the line conductor C325 of the subscriber line 3l5 by way of the contact 301 in the contact bank 300 of the Strowger mechanism included in the connector switch 200, the wiper 302, C293, RA395', C8l5,

, RA362 and the back contact associated therewith,

C814, RA39I' and the front contact associated therewith, CH2, and the upper winding of the ring cut-off relay R360 to battery.

It is noted that the control relay R380 is energized by way of the previously traced circuit from the ring pick-up lead C822 when code ringing is employed in the system at the beginning of a series of transmitted coded impulses so that a complete series of coded impulses of code ringing current is initially transmitted to the called subscriber substation. When energized over this circuit the control relay R380 operates to complete, at RA382 and RA383, a holding circuit for itself extending from ground, at RA268, by way of C283. RA382, RA383, RA354, and the winding of R380 to battery. Also the relay R380 interrupts, at RA383 and R0384, the original circuit for energizing the winding thereof from the ring pick-up lead C822, and prepares, at RA38| and the front contact associated therewith, a pointin the previously traced circuits for projecting ringing current by way of either of the conductors C291 and' C293 to the subscriber substation C connected to the called subscriber tern,

.th ungroundedterminal of a ring back tone transformer winding by way 01' the ring back tone lead C309, RA330, C3", the condenser 319,

C290, the condenser 201, RC243, RA242, C202, and RA! to the conductor CI, and from ground, at RA263, by way 01' R0213, RA212, the lower winding of R260, R0256, RA255, R0243,

RA245, C203, and RA2I2 to the conductor Cl22,

the conductors C|2-1 and CH2 beingconnected together by way of the previously traced loop circuit including the telephone instrument at the calling subscriber substationA. Ring back tone current is returned overthe above-traced circuit to the receiver of the telephone instrument at the calling subscriber substation A, thereby to indicate to the subscriber thereat that ringing current is beng projected over the called subscriber line 3i5, regardless of whether a. divided or bridged ringing circuit is employed in the system. 2

Assuming that harmonic ringing is employed in the system and that the third digit dialed is an odd digit (for example, No. .1), a path is completed at this time for projecting harmonic ring ing current from the conductor terminating at the first contact in the contact bank 329 of the rotary switch 326 by way of the conductor C293 over theline conductor C325 of the subscriber line 3|5, this path extending from the ungrounded terminal of a grounded generator in the source otharmonic ringing current by way 01' the conductor terminating at, the first contact in the contact bank 329 or the rotary switch 326, the

.wiper 321, and the multipled oddcontacts in the contact bank 328 of the rotary switch 326, to the conductor C802. This ringing current is then conducted by way of the previously traced circuit including the line conductor C325 of the subscriber line- 315 to ground at the subscriber substations in the first group in the event that a divided ringing circuit is employed in the sysor to battery at the upper winding of the ring cut-ofi relay R360 in the event that a bridged ringing circuit is employed in the system, as previously noted. It is noted that, when this harmonic ringing current is projected over the line conductor C325 of the subscriber line 3l5, only the ringer at the subscriber substation C which is tuned to the frequency of this harmonic ring ing current is actuated thereby.

Assuming that harmonic ringing is employed in the system and that thethird digit dialed is an even digit (for example, No. 2), the previously traced path is completed at this time for energizing the lower winding of the relay R390 in order to cause operation of this relay, as previously explained. Upon operating, the relay R390 completes the previously traced path for projecting harmonic ringing current from the conductor terminating at the second contact in the contact bank 329 01' the rotary switch 323 by way of the conductor C29l over the linecon- ,ductor C3240! the subscriber line 3| 5, this path extending from the ung'rounded terminal 01' the grounded generator in the source of harmonic ringing current by way of the conductor terminating at the second contact in the contact bank 329 of the rotary switch 326, the wiper 321, and the multipled even contacts in the contact bank 328 to C303. This ringing current is then conducted byway of the previously traced circuit including the line conductor C324 of the subscriber line 3l5 to ground at the subscriber substations in' the second group in the event that a divided ringing circuit is employed in the system, or to battery at the upper winding'of the ring cut-off relay R360 in the event that a bridged ringing circuit is employed in the system, as previously noted. It is noted that, when. this harmonic ringing current is-projected over the line conductor C324 of the subscriber line 3l5, only the ringer at the subscriber substation C which is tuned to the frequency of this harmonicringing current is actuated thereby.

It is noted that the ring control relay R39 is energized by way of the previously traced circuit from the grounded conductor C82l when harmonic ringing is employed in the system. When energized over this circuit the control relay R380 operates, as previously explained, in order to cause ring back tone current to be returned over the previously traced circuit including the loop circuit extending to the calling subscriber substation A..

, The call is answered at the subscriber -substa-.

tion C by removing the receiverof the telephone instrument thereat from its hook, regardless of whether code ringing or harmonic ringing is employed in the system or whether a divided or bridged ringing circuit is employed therein. When the receiver in the telephone instrument at the subscriber substation C is removed from its hook, a bridge including the telephone instrument thereat is connected across the line conductors C324 and C325of the .called subscriber line 3i 5. This bridge across the line conductors of the called subscriber line 3I5 completesa low resistance circuit for energizing the upper winding of the ring cut-01f relay R360. The circuit for energizing the upper winding of the ring cut-off relay R360 is substantiallygidentical to the previously traced circuit for projecting ringing current over the subscriber line 3I5 when a bridged ringing circuit is employed in the system. When thus energized the ring cut-01f relay R360 operates to complete, at RA360, a holding circuit for energizcompletes, at RA364, an obvious circuit for'energizing the relay R355, thereby to cause operation thereof. Further the ring cut-off relay R360 interrupts, at RA36| and the back contact associated therewith, or at RA362 and the back contact associated therewith, a point in the circuit for projecting ringing current over the line conductor C324 or C325 of the subscriber line 3l5. Finally, the ring cut-off relay R360 completes, at RA36I and the front contact associated therewith, and

at RA362 and the front contact associated therewith, a circuit for energizing the battery reversing relay R250, this circuit extending from ground, at the lower winding of R250, by way of the lower winding of R250, C292, RA362 and the front contact associated therewith, CM 5, and RA335' to C293. and from battery at the upper winding of R250 by way of the upper winding of R250, C290, RA36I and the front contact associated therewith, C8l I, and RA395 to C29i, the conductors 029i and C293 being connected together by way of the loop circuit including the called subscriber line M5 and extending to the called subscriber substation C. When energized over the above-traced circuit, the relay R250 operates to reverse the application of battery and ground potentials applied to the conductors Cl2l and C|22 of the trunk line I extending by way of the loop circuit to the calling subscriber substation A, thereby to cause a call registering meter or coin collecting device or the like associated with the calling subscriber line I I5 to be operated. More particularly, the relay R250 completes, at RA25I and RA252, a path for applying ground potential to the conductor CI2I, this path extending from ground, at RA268, by way of RC213, RA212, the lower winding of R280, RA25I,

' RA252, R0243, RA242, C202, and RA2I-I to CHI, and interrupts, at RA252 and RC253, the previously traced circuit for applying battery potential at the upper winding of the relay R260 to the conductor CIZI. Also the relay R250 completes, at RA254 and RA255, a path for applying battery potential to the conductor CI22, this path extending from battery at the upper winding of R260 by way of the upper winding oi. R250, RA254, RA255, R0246, RA245, C203, and RA2I2 to CI22, and interrupts, at RA255 and RC2 58, the previously traced circuit for applying ground potential, at RA268, to the conductor Cl22.

Upon operating, the relay R355 interrupts, at RA358, a point in a circuit traced hereinafter for energizing the release magnet M344 of the Strowger mechanism included in the connector switch 200, and completes, at RA359, a circuit for energizing the release magnet M343 of the minor switch 325, the latter circuit extending from ground at the resistor 209', by way of the resistor 209', C231, RA359, C808, RA381, the switch springs 34I and 342 of the off-normal springs 339 associated with the minor switch 325, and the winding of M343 to battery. When energized over the above-traced circuit the release magnet M343 operates to cause the minor switch 325 to be released and restored by a spring arrangement to its initial position in an extremely short interval of time. When the wipers of the rotary switches included in the minor switch 325 are restored-to their initial positions, the ofi-normal springs 339 associated with the minor switch 325 are actuated in order to move the switch springs 3M and 342 into disengagement, and to move the switch springs 34l and 340 into engagement.

traced hereinafter for energizing the release magnet M344. of the Strowger mechanism included in the connector switch 200 is prepared.

Also, upon operating, the relay R355 completes,

over the loop circuit extending to the calling subscriber substation A.

At this time an established connection is completed between the calling subscriber substation A and the called subscriber substation C, the loop circuit extending to the callingsubscriber substation A being supplied with talking battery by way of the line relay R260, and the loop circuit extending to the called subscriber substation C being supplied with talking battery by way of the battery reversing relay R250, and these loop at RA351, an obvious circuit for energizing the I relay R385, which latter relay, being of the slowto-operate type, does not immediately operate. Shortly thereafter the relay R385 operates in a manner more fully described subsequently, and

thereafter warns the subscribers at the substa- RA354, the circuit for energizingthe relay R380;

thereby to cause the latter relay to restore. Upon restoring, the relay R380 interrupts, at RA380, the circuit for returning ring back tone current circuits being interconnected by means of the voice frequency coupling condensers 201 and 208. More particularly, the conductors C202 and C203 included in the loop circuit extending to the calling subscriber substation A are respectively connected by way of the condensers 201 and 208 to the conductors C290 and C292 included in the loop circuit extending to the called subscriber substation C.

In the event the called line 3l5 is one of a group of trunk lines extending to a central point,

such, for example, as a private automatic branch exchange or P. A. B. X., the connector switch 200 operates automatically to hunt for an idle line in this group of trunk lines in the event the called line 315 is busy. For example, assuming that the called line 3l5 is one of a group of trunk lines extending to a P. A. B. X. and is busy when it is seized by the connector switch 200, the test relay R310 is energized over the previously traced circuit upon the restoration of the relay R280 shortly following the conclusion of the third digit dialed. Also the control wiper 304 carried by the carriage of the Strowger mechanism included in the connector switch 200 engages the contact 3H in the contact bank 300 which is connected by way of the Z wiring illustrated to the control conductor C3l6 of the called line 3l5. Upon operating, the test relay R310 prepares, at RA314, the previously traced circuit for returning busy tone current over the loop circuit extending to the calling subscriber substation A, prepares, at RA312 and the front contact associated therewith, the previously traced holding circuit for itself, interrupts, at RA311. and at RA318, points in the previously traced pulsing circuit for energizing the relay R280 and the rotary magnet M345 of the minor switch 325, and completes, at RA31l, a circuit for energizing the lower winding of the relay R390, this circuit extending from the grounded control conductor C3l6 of the called line 3l5 by way of the Z wiring illustrated, the contact 3| I, the control wiper 304, Cl, RA31I, RA346, C291, R0394, RA394, MA346, and the lower winding of R390 to battery. When energized over the above-traced circuit the relay R390 operates to complete, at RA393 and RA394, the previously traced holding'circuit for itself, and completes, at RA393, an alternative circuit for energizing in multiple the relay R345 and the rotary magnet M346 of the Strowger mechanism included in the connector switch 200, this circuit extending from ground, at RA288, by way of C283, RA398', C2l6, RA216, RC218, C289 and RA393 to the conductor C288, one branch of this circuit extending from the conductor C288 by way of RA282 and the back contact associated therewith, and the winding of R345 to battery, and the other branch of this circuit extending from the conductor C288 by way of the winding of M348 to battery. When energized over the abovetraced circuit the relay R345 remains in its 0perated position, thereby to retain interrupted, at RA345, the previously traced circuit for returning 

